A semiconductor memory device may be embodied using semiconductor, such as silicon Si, germanium Ge, gallium arsenide GaAs, indium phosphide InP, etc. A semiconductor memory device may be classified into a volatile memory device and a nonvolatile memory device.
A volatile memory device loses its stored data when its power supply is interrupted. Examples of a volatile memory device are a static RAM (SRAM), a dynamic RAM (DRAM), a synchronous DRAM (SDRAM), etc. A nonvolatile memory device retains its stored data even when its power supply is interrupted. Examples of a nonvolatile memory device are a read only memory (ROM), a programmable ROM (PROM), an electrically programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a flash memory device, a phase-change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), a ferroelectric RAM (FRAM), etc.
As semiconductor integration technology is improved, an interconnection space between word lines and bit lines in a semiconductor chip is becoming small. Problems such as reliability degradation and performance degradation of a semiconductor memory device occur due to an increase of coupling between interconnections.